BTEX pollution caused by motorcycles in the megacity of HoChiMinh

JOURNAL OFENVIRONMENTALSCIENCES

ISSN 1001-0742

CN 11-2629/X

www.jesc.ac.cn

Available online at www.sciencedirect.com

Journal of Environmental Sciences 2013, 25(2) 348–356

BTEX pollution caused by motorcycles in the megacity of HoChiMinh

Tran Thi Ngoc Lan∗, Pham Anh Minh

University of Science, Vietnam National University, 227 Nguyen Van Cu, HoChiMinh 70000, Vietnam

Received 29 April 2012; revised 12 September 2012; accepted 25 September 2012

AbstractMonitoring of benzene, toluene and xylenes (BTEX) was conducted along with traffic counts at 17 roadside sites in urban areas of

HoChiMinh. Toluene was the most abundant substance, followed by p,m-xylenes, benzene, o-xylene and ethylbenzene. The maximum

observed hour-average benzene concentration was 254 μg/m3. Motorcycles contributed to 91% of the traffic fleet. High correlations

among BTEX species, between BTEX concentrations and the volume of on-road motorcycles, and between inter-species ratios in

air and in gasoline indicate the motorcycle-exhaust origin of BTEX species. Daily concentrations of benzene, toluene, ethylbenzene,

p,m-xylenes and o-xylene were 56, 121, 21, 64 and 23 μg/m3, respectively. p,m-xylenes possess the highest ozone formation potential

among the BTEX family.

Key words: air pollution; benzene; BTEX; HoChiMinh; motorcycle exhaust

DOI: 10.1016/S1001-0742(12)60045-X

Introduction

Rapid global industrialisation in the last half-century has

resulted in a rapid increase in the urban population and the

formation of megacities with high population and popu-

lation density. This phenomenon has been most dramatic

on the least-urbanised Asian and African continents. Cur-

rently, Asia alone has more than 10 megacities, including

Shanghai, China (23 million, 2011), Beijing, China (19.6

million, 2011), Dhaka, Bangladesh (16 million, 2011),

Tokyo, Japan (13 million, 2011), Karachi, Pakistan (13

million), Delhi, India (12.8 million, 2011), Guangzhou,

China (12.7 million, 2011), Mumbai, India (12.5 million,

2011), Manila, the Philippines (11.5 million, 2009), Seoul,

Korea (10.6 million, 2011) and Jakarta, Indonesia (10.2

million, 2011). Most of the megacities in developing

countries are currently experiencing serious air pollution

by particulate matter and volatile organic carbons (VOCs)

due to the uncontrolled expansion of private means of

transportation. Among the VOC pollutants, special atten-

tion has been paid to BTEX species, especially to benzene,

due to their adverse effects on human health. A main

source of BTEX in urban areas is gasoline evaporation

and vehicle emission. It is accepted that benzene is a

human carcinogen (US EPA, 2012). The risk of leukaemia

by lifetime exposure to benzene at 17, 1.7 and 0.17

* Corresponding author. E-mail: [email protected]

μg/m3 is, respectively, 10−4, 10−5 and 10−6 (WHO, 2000).

Additionally, benzene and other aromatic hydrocarbons

also contribute to the formation of ground ozone, pho-

tochemical smog and toxic peroxyacylnitrates through

atmospheric photochemical processes. Benzene is highly

toxic; therefore, the WHO and US EPA do not specify any

save level for benzene exposure. The Vietnamese National

Air Quality Standards (NAQS) for time-weighted average

hour and annual ambient concentrations of benzene are 22

and 10 μg/m3, respectively.

Benzene pollution is an important issue for the

megacities of developing countries. The annual aver-

age roadside benzene concentration in Delhi, India was

(86.47 ± 53.24) μg/m3 in 2001–2002, and has increased

continuously despite the full implementation of com-

pressed natural gas (CNG) in a the public transportation

system in December 2002. Average benzene concentra-

tions of the pre- and post-CNG periods at two traffic

intersections in Delhi were (116.32 ± 51.65) and (187.49 ±22.50) μg/m3, respectively. The reason for these enhanced

concentrations has been solely attributed to the increase in

the vehicular population from 3.5 million in 2001–2002

to 5.1 million in 2007 (Khillare et al., 2008). Benzene

concentrations have been found to be 67 μg/m3 in Cairo,

Egypt (Khoder, 2007), 14.7 μg/m3 in Mumbai, India

(Gauri et al., 2011), 11.8 μg/m3 in Manila; the Philippines

(Balanay and Lungu, 2008); 51.5 μg/m3 in Guangzhou,

China (Wang et al., 2002) and 27 μg/m3 in Algiers, Algeria

No. 2 BTEX pollution caused by motorcycles in the megacity of HoChiMinh 349

(Rabah et al., 2006).

HoChiMinh has a population of around 8.5 million,

and is the financial, industrial and commercial centre

of Vietnam. Urban transportation in HoChiMinh, like in

any urban area in Vietnam, depends on motorcycles. The

motorcycle and automobile populations in the city in

March 2008 were 3,444,868 and 346,355, respectively;

these numbers increased to 3.9 million and 386,000,

respectively, in June 2009. The estimated number of mo-

torcycles in the middle of 2012 is around 5 million. A

large number of vehicles employ old technology. Traffic

volume is extremely high and traffic jams are frequent; as a

consequence, pollution by VOC and particulate matter has

resulted in a dramatic decline in air quality. VOC monitor-

ing is not obligatory in Vietnam, hence VOCs have been

desultorily monitored in Hanoi and HoChiMinh through

some short-term programmes carried out by the EPA or

university research groups. A study on 73 hydrocarbons

and chlorinated hydrocarbons at nine sites in HoChiMinh

in 2002 using Compendium Method TO-15 (US EPA,

1999) revealed a high total VOC concentration of 1262

ppbv and a benzene concentration of 63 ppbV (Lan et

al., 2006). The weekly average benzene concentrations

measured by the HoChiMinh EPA using Radiello passive

samplers on six streets in HoChiMinh in July 2008–

June 2009 were 7.9–72.9 μg/m3 (HoChiMinh EPA, 2009),

additionally, benzene concentrations at all sites in the first

half of 2009 were 1.07–1.46 times higher than those in the

first half of 2008. Hanoi is the capital city of Vietnam with

a population of 3.5 million. Truc and Oanh (2007) reported

a roadside benzene level of 65 μg/m3 on a busy street in

Hanoi. The EURO II standard came into effect in Vietnam

in July 2008.

This study aimed to investigate roadside BTEX in urban

areas in HoChiMinh and the impact of different means of

transportation on BTEX pollution.

1 Materials and methods

1.1 Sampling sites

Samples were collected at 17 sites (S1–S17) located on

main roads in nine residential districts (Fig. 1). All sites

have wide pavement for pedestrians. Sites S13–S17 are

located in the central district of HoChiMinh.

1.2 Sampling and analyses

The NIOSH 1501 method (NIOSH, 2003) using ac-

tive sampling and solvent extraction was applied for

air sampling. Sample tubes containing 200 mg of acti-

vated charcoal were purchased from Sibata (Japan). A

programmable minipump (MP∑

30, Sibata, Japan) was

calibrated using a bubble flow meter. A breakthrough

experiment was conducted by pumping air at a flow of

130 and 150 mL/min in 56 min through two sample tubes

connected in series. Sampling was done during rush hour

Fig. 1 Locations of sampling sites (S1–S17).

at the entrance of a university motorcycle park. Sample

tubes were sealed with polypropylene caps and sent to the

laboratory. The charcoal was transferred into GC vials and

extracted with 1 mL of benzene-free carbon disulphide

containing fluorobenzene and chlorobenzene as the inter-

nal standards. The transfer was performed in a glove box

filled with zero air. Vials were shaken occasionally for 45

min, and left for 1 hr in a refrigerator for the charcoal to

settle. Aliquots were quantified using a Hewlett Packard

HP 5890 II gas chromatograph equipped with a flame

ionisation detector, an autosampler and an HP-5MS 30.0

m × 0.25 mm × 0.25 μm column. An amount of any BTEX

species in the second tube was not more than 0.9% of

that in the first tube, confirming the applicability of the

sampling procedure.

Sampling at sites was performed on work days in the

fourth quarter of 2009. Sampling was performed at a flow

rate of 130 mL/min in 56 min. The total sampling volume

was 7.41–7.42 L. Sampling was carried out each hour

consecutively for 24 hr at site S1; during rush hour (7:00–

8:00 and 17:00–18:00) and non-rush hour (12:00–13:00)

at sites S2–S13; and from 8:00–9:00 at the remaining

sites. The inlet of sample tube was placed 1.7 m above

the ground and 1.5 m away from the roadside. In total,

64 samples were collected. A blank was transported to

the sampling sites and back to the laboratory. Samples

were sealed with polypropylene caps, kept in an air-

tight polypropylene tube packed in a aluminium zippered

laminar envelope and cold-stored until analysis.

Samples were analysed within one week of sampling.

Analysis was carried out as reported above. The concen-

tration of a pollutant in air (C, μg/m3) was evaluated using

350 Journal of Environmental Sciences 2013, 25(2) 348–356 / Tran Thi Ngoc Lan et al. Vol. 25

the following equation:

C =Ws − Wb

V × DE× 1000

where, Ws (μg) and Wb (μg) are the collected and the blank

amount of the pollutant by analysis, V (L) is sampling

volume and DE is the desorption efficiency. DE was given

by the manufacturer for each lot of activated charcoal and

was 98% in this study.

Two gasoline types marketed in Vietnam, RON92 and

RON95, were analysed. Gasoline was diluted in benzene-

free carbon disulphide containing internal standards and

injected into the gas chromatograph for quantification.

1.3 Traffic observation

Traffic was recorded by a video camera. Record-

ed videos were replayed for traffic counts. Means of

transportation were divided into the following groups:

motorcycles, under 9-seat cars, 12–24-seat passenger cars,

above 25-seat passenger cars, light-duty trucks and heavy-

duty trucks.

2 Results and discussion

2.1 Hour-average BTEX concentrations

Toluene was the most abundant species, followed by

p,m-xylenes (p,m-X), benzene (B), o-xylene (o-X) and

ethylbenzene (E) in all samples. Figure 2 shows the

diurnal variation in hour-average BTEX concentrations at

site S1. Pollutant levels were high in the daytime and low at

night. Peaks were observed during rush hour at 7:00–9:00

and 17:00–18:00. The benzene concentration was lower

than the NAQS only for a short period of time at night

from 0:00–5:00. Daily average concentrations of benzene,

toluene, ethylbenzene, p,m-xylenes and o-xylene at site S1

were, respectively, 56, 121, 21, 64 and 23 μg/m3.

The BTEX concentrations at 17 sites are reported in Fig.3. Commonly, BTEX concentrations were low at midday

and high during rush hour, and they were higher in the

afternoon than in the morning. High BTEX concentrations

were observed at sites S1, S6, S7, S8, S9 and S11 lo-

cated on narrow roads with dense traffic fleets and high

buildings. All observed benzene concentrations during the

day were higher than the NAQS. Maximum hour-average

concentrations of benzene, toluene, ethylbenzene, p,m-

xylenes and o-xylene were 254, 619, 95, 263 and 116

μg/m3, respectively.

2.2 Relationships between benzene and C1,C2-benzene

The inter-species ratios of BTEX pollutants depend on fuel

composition, sources, climatic conditions as well as the

age of air parcels since BTEX species sink at different

rates under sunlight due to their different photochemical

activities. Inter-species ratios are an important indicator of

sources. A main source of BTEX species in urban areas

is vehicle emission. It is accepted that benzene originates

from traffic emissions and gasoline evaporation only, while

other BTEX species may be airborne from other addition-

al sources like industry or construction. C1,C2-benzene/

benzene (C1,C2-B/B), especially toluence/benzene (T/B)

ratios, are often used to identify sources. T/B values below

3 have been found to be characteristic of traffic emissions

worldwide, including in Vietnam and China (Perry and

Gee, 1995; Brocco et al., 1997; Heeb et al., 2000b; Monod

et al., 2001; Chan et al., 2002; Hiesh et al., 2006; Kumar

and Tyagi, 2006; Khoder, 2007; Truc and Oanh, 2007;

Hoque et al., 2008; Liu et al., 2009; Matysik et al., 2010).

T/B values of 1.5–4.3 are considered an indicator of traffic

emissions, as reported by Hoque et al. (2008) and Liu et al.

(2009). For T/B values > –4.3, solvent source impacts are

likely. A specific B/T ratio below 0.20 has been proposed

and used as an indicator of samples strongly affected

by industrial emissions in Dongguan, China (Barletta et

al., 2008), while a ratio of 0.4–1.0 has been used as an

indicator of air propelled by vehicular exhaust in Beijing

(Wang et al., 2012). T/B > 4.3 was used to identify sources

50

100

150

200

250

300

Conce

ntr

atio

n (

μg/m

3)

Benzene

Toluene

Ethylbenzene

p,m-Xylenes

o-Xylene

0-

1

1-

2

2-

3

3-

4

4-

5

5-

6

6-

7

7-

8

8-

9

9-1

0

10 -

11

11-

12

12-

13

13-

14

14-

15

15-

16

16-

17

17-

18

18-

19

19-

20

20 -

21

21-

22

22-

23

23-

24

Time

Fig. 2 Diurnal variation of BTEX concentrations at roadside in HoChiMinh City.


0

50

100

150

200

250

300

S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17

BenzeneTraffic jam

0

100

200

300

400

500

600

700


Toluene

0

20

40

60

80

100


Ethylbenzene

0

50

100

150

200

250

300


p,m-Xylene

7:00-8:00 12:00-13:008:00-9:00 17:00-18:00

0

50

100

150

200

250

300


Co

ncentr

ati

on (

μg

/m3) o-Xylene

Co

ncentr

ati

on (

μg

/m3)

Co

ncentr

ati

on (

μg

/m3)

Co

ncentr

ati

on (

μg

/m3)

Co

ncentr

ati

on (

μg

/m3)

Fig. 3 BTEX concentrations at the sampling sites during different sampling campaigns.

influenced by solvent use in Windsor, Ontario, Canada (Xu

et al., 2010). A high T/B ratio (8.6) in a neighbourhood

of an industrial park in Taiwan suggested large additional

sources of toluene from industry (Hiesh et al., 2006). An

overview of inter-species ratios between BTEX species in

different environments in Asia, Europe and South America

was provided by Monod et al. (2001). A T/B value of 2.3

(R2 = 0.91) and a B/E value of 2.16 (R2 = 0.87, E/B = 0.46)


y = 2.269x

R2 = 0.924

y = 0.366x

R2 = 0.945

0

100

200

300

400

500

600

0 50 100 150 200 250 300

Conce

ntr

atio

n (

μg/m

3)

Benzene concentration (μg/m3) Benzene concentration (μg/m3)

Toluene

Ethylbenzene

y = 1.059x

R2 = 0.967

y = 0.439x

R2 = 0.951

0

50

100

150

200

250

300

0 100 200 300

Conce

ntr

atio

n (

μg/m

3)

p,m-Xylene

o-Xylene

Fig. 4 The correlation between benzene and other BTEX species.

were reported for a traffic microenvironment.

A good linear correlation between concentrations of

benzene and other BTEX species at all sites (Fig. 4)

indicates a same main source of BTEX species. The

contents of benzene, toluene, ethylbenzene, p,m-xylenes

and o-xylene in RON92 and RON95 gasoline were 1.81,

4.55, 0.30, 1.21, 0.45 and 1.85, 4.20, 0.54, 1.70 and 0.77

wt.%, respectively. Thus, the T/B, E/B, p,m-X/B and o-X/B

ratios in A92 and A95 gasoline were 2.5, 0.17, 0.7 and 0.25

and 2.3, 0.29, 0.9 and 0.42, respectively. The C1,C2-B/B

values obtained in roadside air were very close to those

in A95 gasoline. All these findings confirm that traffic

emission is the main source of BTEX alongside roads in

HoChiMinh.

2.3 Diurnal variation of inter-species ratios

The diurnal variation in inter-species ratios is shown in

Fig. 5. Roadside BTEX originates from fresh vehicle

emissions, so their inter-species ratios should be close to

those in vehicle emissions. The observed diurnal variation

in inter-species ratios was possibly related to a variation in

the constituents of a traffic fleet. The p,m-X/E ratio was

almost unchanged throughout the day, while the o-X/E

and p,m-X/o-X ratios increased at night. A clear increase

in the C1,C2-B/B and T/C2-B ratios at night was due

to the increased contribution of trucks in the traffic fleet

as reported below. Another reason is likely an increase

in the contribution of toluene released from construction

painting or solvent use due to low traffic volume at night.

The elevated T/C2-B ratio from 11:00 –12:00 at site S1

was possibly due to nearby biomass burning in household

cooking. According to Monod et al. (2001), T/B and T/E

ratios in biomass burning environment are 0.45 and 9.41.

The T/p,m-X and T/o-X ratios for biomass burning have

not been reported, but they can be easy evaluated from the

m-X/p-X, m-X/o-X, m-X/E and T/E ratios. The evaluated

T/p,m-X and T/o-X ratios for biomass burning are 8.9

and 8.5, much higher than for traffic emission. Thus, a

contribution from biomass burning would result in an

increase in the T/C2-B ratio.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Mas

s ra

tio t

o b

enze

ne Toluene

Ethylbenzene

p,m-Xylene

o-Xylene

Ethylbenzene

p,m-Xylene

o-Xylene

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

Mas

s ra

tio o

f to

luen

to o

ther

s

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10 -

11

11-

12

12-

13

13-

14

14-1

5

15-

16

16-

17

17-

18

18-

19

19 -

20

20 -

21

21-

22

22 -

23

23-

24

Mas

s ra

tio

p,m-Xylenes/Ethylbenzene

o-Xylene/Ethylbenzenep,m-Xylenes/o-Xylene

Time

Fig. 5 Diurnal variation in the inter-species ratios.

2.4 Relationship between BTEX and traffic

Figure 6 shows the BTEX concentrations and traffic

volumes at site S1. Traffic volume was extremely high at

10,500–22,300 vehicles/hr during the day, and decreased to

780–16,600 vehicles/hr at night. It was low at 0:00–5:00.

Motorcycles contributed to 74%–97% of the traffic fleet,

with an average of 92.5%. The constituents of the traffic

fleet varied during the day. Heavy trucks were only seen at

night since they are allowable in the city only from 20:00–

6:00, according to local traffic regulations.

Traffic volumes at other sites were 880–22,876 vehi-

cles/hr. Traffic jams were seen at sites S4 and S7 in


0

5000

10000

15000

20000

25000

0

20

40

60

80

100

120

140

Tra

ffic

volu

me

(veh

icle

s/hr)

Ben

zene

(μg/m

3)

Tolu

ene

(μg/m

3)

0

5000

10000

15000

20000

25000

0

50

100

150

200

250

300

Tra

ffic

volu

me

(veh

icle

s/hr)

0-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10 -

11

11-

12

12-

13

13-

14

14-1

5

15-

16

16-

17

17 -

18

18-

19

19-

20

20 -

21

21-

22

22 -

23

23-

24

0-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-1

0

10

-1

1

11-

12

12-

13

13 -

14

14-1

5

15 -

16

16-

17

17 -

18

18-

19

19-

20

20

-2

1

21-

22

22-

23

23-

24

Time Time

Fig. 6 BTEX concentrations and traffic volume at Site 1.

the afternoon rush hours. Motorcycles were always the

predominant means of transportation. The contribution

of motorcycles was the lowest (58%–86%) at site S13,

located in the city centre and surrounded by luxury hotels

and shopping malls. The contribution of motorcycles at

other sites was 83%–98%. The average contribution of

motorcycles in the traffic fleet in the whole city was 91%.

This is the same as the motorcycle population within the

total vehicle population in the city.

The correlation between benzene and toluene concentra-

tions and traffic volume at site S1 is clearly seen in Fig. 6.

The correlation coefficients (R2) for the linear regression of

BTEX concentration versus number of motorcycles in the

traffic fleet at all sites were 0.595, 0.455, 0.559, 0.574 and

0.548, respectively, for benzene, toluene, ethylbenzene,

p,m-xylenes and o-xylene. The impact of different means

of transportation on BTEX pollution are summarised in

Table 1. These relationships between the total concen-

tration of BTEX species and the number of motorcycles

point out that the biggest contributor to roadside BTEX in

HoChiMinh is motorcycle exhaust.

2.5 Ozone formation potential of BTEX species

Ozone formation potential can be evaluated using Carter’s

maximum incremental reactivity (MIR). Unitless MIR is

the amount of ozone formed when one gram of VOC is

added to an initial VOC-NOx mixture under relatively high

NOx conditions (Carter, 1990, 1994). It was impossible

to evaluate the daily-average BTEX concentration for the

city; therefore, ozone formation potentials were evaluated

from the daily-average concentrations of benzene, toluene,

ethylbenzene, p,m-xylenes and o-xylene at site S1 and are

given in Table 2. Among the BTEX species, p,m-xylenes

were the biggest contributors to ozone formation followed

by toluene, while benzene was the lowest contributor.

2.6 Comparison of BTEX pollution in HoChiMinh andin other cities

Benzene is monitored and controlled throughout the world.

Table 3 summarises roadside benzene concentrations re-

ported in the literature. Antwerp (Belgium), Melbourne

(Australia) and Tokyo (Japan) are considered clean.

Guangzhou (China), HoChiMinh, Hanoi (Vietnam), Cairo

(Egypt) and Delhi (India) are badly polluted with benzene.

Vehicle exhaust is the main source of BTEX in the above

mentioned polluted cities, except in Guangzhou. Traffic in

HoChiMinh, Hanoi, Cairo and Delhi is characterised by

very high traffic volume and a high number of motorcycles

in the traffic fleet. The contribution of motorcycles in the

traffic fleet has been found to be 91% in HoChiMinh

(this study), 94%–96% in Hanoi (Truc and Oanh, 2007)

and 63% in Delhi (Hoque et al., 2008). Motorcycles are

an important means of transportation in Cairo, with a

motorcycle population of 300,000. Most motorcycles in

Delhi and Cairo are two-stroke engines (Hoque et al.,

2008; CAIP, 2000), while over 95% of motorcycles in

Table 1 Correlation coefficient (R2) between BTEX concentrations and traffic volumes

Motorcycles 4–9-seat cars 12–24-seat cars 25–50-seat cars Light trucks Heavy trucks

For site S1 0.783 0.551 0.347 0.441 0.034 0.171

For all sites 0.529 0.011 0.001 0.095 0.002 0.004

Table 2 Ozone formation potential

Hydrocarbon Benzene Toluene Ethyl benzene m,p-Xylenes o-Xylene

Daily-average concentration at site S1 (μg/m3) 56 121 21 64 23

MIR 0.42 2.70 2.70 8.20 6.50

O3 formation potentiala (μg/m3) 24 327 57 525 150

aVOC (μg/m3) × MIR.


Table 3 Benzene concentrations in some cities in the world

City Benzene Reference

Antwerp, Belgium 2.5 Buczynska et al., 2009

Melbourne, Australia 2.8–3.6 EPA Victoria, 2006

(0.85–1.1 ppb)

Tokyo, Japan 3–7 Laowagul et al., 2009

UK Up to 6.3 UK DEFRA, 2012

(1.9 ppb)

Nanjing, China 6.4 Wang and Zhao, 2008

Christchurch, New Zealand 5.65 –9.10 Myles, 2005

Kathmandu, Nepan 13–20 Chiranjibi, 2004

Nanhai, China 20.0 Wang et al., 2002

Hongkong, China 26.7 Chan et al., 2002

Bangkok, Thailand 35 Leong et al., 2002

Macau, China 34.9 Wang et al., 2002

Guangzhou, China 51.5 Wang et al., 2002

HoChiMinh, Vietnam 56 This study

Hanoi, Vietnam 65 Truc and Oanh, 2007

Cairo, Egipt 67 Khoder, 2007

Dehli, India 87 Hoque et al., 2008

Hanoi and HoChiMinh are four-stroke engines. There are

numerous reasons for the high BTEX levels in the above

mentioned urban areas: high traffic volume, a high number

of motorcycles in the traffic fleet, high benzene content

in gasoline and a high emission factor for motorcycles.

The current benzene content in gasoline is ca. 1.8 wt.%

in Vietnam, almost double the 1% in the US, Europe and

Japan. Motorcycles do not have any exhaust gas treatment

system; hence, a motorcycle emits much more benzene

than a gasoline-powered car equipped with a converter.

Our research on 23 in-use motorcycles in HoChiMinh

showed average emission factors of benzene, toluene,

ethylbenzene and xylenes at 105, 195, 32 and 137 mg/km

with geometric values of 61, 118, 16, 49 and 18 mg/km and

median values of 54, 142, 21, 66 and 23 mg/km (Lan et

al., 2010). The benzene emission factor (BEF) was much

higher than the BEFs of 3.8 mg/km, 5.9–17 mg/km and

12.2 mg/km found for catalytic-converter cars in Europe,

the US and Japan, respectively; almost the same BEF range

of 71–96 mg/km has been found for pre-catalyst cars in the

US (Heeb et al., 2000a; Dasch and Williams, 1991; Kaga

et al., 2004).

Inter-species ratios of BTEX species for traffic-related

sites are similar to those in vehicle exhaust due to a short

spatial and temporal distance from sources. They depend

mainly on fuel composition and vehicle technology. The

average T/B ratio was about 2.3 in this study, 1.8–2.54

in Delhi (Hoque et al., 2008), 0.7–1.3 in Hanoi (Truc and

Oanh, 2007) and 1.29–2.45 in Cairo (Khoder, 2007). The

above mentioned values were lower than values common-

ly found in developed countries such as 3.7 in Naples

(Pasquale et al., 2009), 3.8–4.4 in Antwerp (Buczynska

et al., 2008), 6.4–8.5 in Tokyo (Hoshi et al., 2008) and

9.2–11.5 in Hong Kong (Ho et al., 2004). The E/B values

in this study were around 0.38, in the same range of

0.23–0.43 found in Hanoi (Truc and Oanh, 2007). They

were remarkably lower than the E/B values of 1.2 and 1.0

found for roadsides in Tokyo (Hoshi et al., 2008) and in

Bangkok (Laowagul et al., 2008), respectively, but higher

than 0.15–0.21 found in Delhi (Hoque et al., 2008). The

same phenomenon was observed for the p,m-X/B and o-

X/B ratios. The p,m-X/B and o-X/B values in HoChiMinh

were 1.06 and 0.44, respectively; these values were much

lower than 2.1 and 0.8 found in Tokyo (Hoshi et al., 2008),

but higher than 0.64–0.87 and 0.31–0.47 found in Delhi

(Hoque et al., 2008).

In this study, the interspecies ratios for roadside air

were similar to those in gasoline. The low C1,C2-

benzene/benzene ratios in HoChiMinh, Hanoi, Delhi and

Cairo are possibly related to the composition of gasoline

available locally. One possible reason that could lower

the C1,C2-benzene/benzene ratio is evaporation from the

gasoline tanks of cheaply made motorcycles with the high

atmospheric temperatures in hot tropical regions. Benzene

vapour pressure is higher than that of other BTEX species,

so according to Raoul’s law, its content in a vapour is richer

than in a liquid mixture.

From the discussion above, it is clear that the inter-

species ratios in both the gas phase and liquid fuel are

important for the assessment of sources.

3 Conclusions

(1) Roadside BTEX levels were monitored at 17 urban

sites in HoChiMinh. All the observed hour-average ben-

zene concentrations during the day were much higher than

the NAQS of 22 μg/m3. The maximum observed benzene

level was 254 μg/m3.

(2) Traffic emission is the main source of roadside

BTEX in HoChiMinh. Motorcycles are the biggest con-

tributor to BTEX pollution in HoChiMinh.

(3) Daily concentrations of benzene, toluene, ethylben-

zene, p,m-xylene and o-xylene in HoChiMinh were 56,

121, 21, 64 and 23 μg/m3, respectively.

(4) BTEX pollution in Vietnam is characterised by a

high benzene level and low C1,C2-benzene/benzene ratios.

The inter-species ratios of BTEX species in roadside air

and in gasoline are similar.

Acknowledgments

This research was supported by Vietnam National Univer-

sity, HoChiMinh City and Vietnam National Foundation

for Development of Science and Technology. The authors

would like to express their sincere appreciation to Dr.

Torbend Lund, Roskilde Universitet Center, Denmark for

the GC system. They are grateful to Prof. Akikazu Kaga,

Dr. Akira Kondo from Osaka University, Japan; Dr. Kyoshi

Imamura from Jica; for their valuable advice and collabo-

ration. Many thanks to Core-University JSPS Program and

Japan Society for Environmental Chemistry for the support

for visits to Japan and International Conferences during

this study.


References

Balanay J A G, Lungu C T, 2008. Exposure of Jeepney drivers in

Manila, Philippines, to selected volatile organic compounds

(VOCs). Industrial Health, 47(1): 33–42.

Barletta B, Meinardi S, Simpson I J, Zou S, Rowl S, Blake D R,

2008. Ambient mixing ratios of nonmethane hydrocarbons

(NMHCs) in two major urban centers of the Pearl River

Delta (PRD) region: Guangzhou and Dongguan. Atmo-spheric Environment, 42(18): 4393–4408.

Brocco D, Fratarcangeli R, Lepore L, Petricca M, Ventrone I,

1997. Determination of aromatic hydrocarbons in urban air

of Rome. Atmospheric Environment, 31(4): 557–566.

Buczynska A J, Krata A, Stranger M, Godoi A F L, Kontozova-

Deutsch V, Bencs L et al., 2009. Atmospheric BTEX-

concentrations in an area with intensive street traffic.

Atmospheric Environment, 43(2): 311–318.

CAIP (Cairo Air Improvement Project).

Vehicle Emissions Testing Component.

http://pdf.usaid.gov/pdf−docs/PNACY042.pdf.

Carter W P L, 1990. A detailed mechanism for the gas-phase

atmospheric reactions of organic compounds. AtmosphericEnvironment. Part A. General Topics, 24(3): 481–518.

Carter W P L, 1994. Development of ozone reactivity scales for

volatile organic compounds. Journal of the Air & WasteManagement, 44(7): 881–899.

Chan C Y, Chan L Y, Wang X M, Liu Y M, Lee S C, Zou S

C et al., 2002. Volatile organic compounds in roadside mi-

croenvironments of metropolitan Hong Kong. AtmosphericEnvironment, 36(12): 2039–2047.

Chiranjibi G, 2004. Air Quality Monitoring and

Management in Kathmandu, Nepal. In: Report of

Ministry of Population and Environment of Nepal,

presented at the Better Air Quality Conference.

cleanairinitiative.org/portal/system/files/59132−gautam.ppt.

Dasch J M, Williams R L, 1991. Benzene exhaust emissions from

in-use General Motors vehicles. Environmental Science &Technology, 25(5): 853–857.

EPA Victoria, 2006. Review of air quality near major

roads. In: Publication 1025 of EPA Victoria, State

Government of Victoria. http://epanote2.epa.vic.gov.au/

epa/publications.nsf/2f1c2625731746aa4a256ce90001cbb5/

c7684b4a679f16a6ca256ee0007c019a/$FILE/1025.pdf.

Gauri G P, Sanjay K S, Vijay D P, 2011. Distribution and source

apportionment of atmospheric non-methane hydrocarbons

in Mumbai, India. Atmospheric Pollution Research, 2(2):

231–236.

Heeb N V, Forss A M, Bach C, Mattrel P, 2000. Velocity-

dependent emission factors of benzene, toluene and C2-

benzenes of a passenger car equipped with and without a

regulated 3-way catalyst. Atmospheric Environment, 34(7):

1123–1137.

Heeb N V, Forss A M, Bach C, Reimann S, Herzog A, Jackle

H W, 2000. A comparison of benzene, toluene and C2-

benzene mixing ratios in automotive exhaust and in the

suburban atmosphere during the introduction of catalytic

converter technology to the Swiss Car Fleet. AtmospherciEnvironment, 34(19): 3103–3116.

Hiesh L T, Yang H H, Chen H W, 2006. Ambient BTEX and

MTBE in the neighborhoods of different industrial parks in

Southern Taiwan. Journal of Hazardous Materials, 128(2-

3): 106–115.

Ho K F, Lee S C, Guo H, Tsai W Y, 2004. Seasonal and diurnal

variations of volatile organic compounds (VOCs) in the

atmosphere of Hong Kong. Science of Total Environment,322(1-3): 155–166.

HoChiMinh EPA, 2009. Air quality. In: Annual report for FY

2009 of Environmental Protection Agency. HoChiMinh,

Vietnam.

Hoque R R, Khillare P S, Agarwal T, Shridhar V, Balachandran S,

2008. Spatial and temporal variation of BTEX in the urban

atmosphere of Delhi, India. Science of Total Environment,392(1): 30–40.

Hoshi J, Amano S, Sasaki Y, Korenaga T, 2008. Investigation and

estimation of emission sources of 54 volatile organic com-

pounds in ambient air in Tokyo. Atmospheric Environment,42(10): 2383–2393.

Kaga A, Kondo A, Shi S, Inoue Y, Thao N T P, Viet P H,

2004. Estimation of cancer risk by benzene emitted from

vehicles. Annual Report of FY 2004 of the Core Univer-

sity Program between Japan Society for the Promotion of

Science (JSPS) and Vietnamese Academy of Science and

Technology (VAST).

Khillare P S, Hoque R R, Shridhar V, Agarwal T, Balachandran S,

2008. Temporal variability of benzene concentration in the

ambient air of Delhi: A comparative assessment of pre-and

post-CNG periods. Journal of Hazardous Materials, 154(1-

3): 1013–1018.

Khoder M I, 2007. Ambient levels of volatile organic compounds

in the atmosphere of Greater Cairo. Atmospheric Environ-ment, 41(3): 554–566.

Kumar A, Tyagi S K, 2006. Benzene and toluene profiles in

ambient air of Delhi as determine by active sampling and

GC analyses. Journal of Scientific and Industrial Reserach,

65(3): 252–257.

Lan T T N, Binh N T T, Imamura K, Maeda Y, 2006. Air pollu-

tants in vietnam - Investigation of concentration of volatile

organic compounds in HoChiMinh. In: Proceedings of the

5th Scientific Conference of Vietnam National University,

HoChiMinh City. HoChiMinh, Vietnam. 26 October.

Lan T T N, Binh N T T, Minh P A, Minh N H N, Kondo A,

Kaga A, 2010. Real-world emission factors of benzene,

toluene, ethylbenzene and xylenes from motorcycles. In:

Proceedings of the 19th Symposium on Environmental

Chemistry: 210–211. Chubu, Japan. 21–23 June.

Laowagul W, Garivait H, Limpaseni W, Yoshizumi K, 2008. Am-

bient air concentrations of benzene, toluene, ethylbenzene

and xylene in Bangkok, Thailand during April-August in

2007. Asian Journal of Atmospheric Environment, 2(1): 14–

25.

Laowagul, W, Yoshizumi K. Behavior of benzene and 1,3-

butadiene concentrations in the urban atmosphere of Tokyo,

Japan, 2009. Atmospheric Environment, 43(12): 2052–

2059.

Leong S T, Muttamara S, Laortanakul P, 2002. Influence of

benzene emission from motorcycles on Bangkok air quality.


Liu J, Mu Y, Zhang Y, Zhang Z, Wang X, Liu Y et al., 2009.

Atmospheric levels of BTEX compounds during the 2008

Olympic Games in the urban area of Beijing. Science of the


Total Environment, 408(1): 109–116.

Matysik S, Ramadan A B, Schlink U, 2010. Spatial and tem-

poral variation of outdoor and indoor exposure of volatile

organic compounds in Greater Cairo. Atmospheric PollutionResearch, 1(2): 94–101.

Monod A, Sive B C, Avino P, Chen T, Blake D R, Sherwood

R F, 2001. Monoaromatic compounds in ambient air of

various cities: a focus on correlations between the xylenes

and ethylbenzene. Atmospheric Environment, 35(1): 135–

149.

Myles M, 2005. Concentrations of benzene, toluene,

ethylbenzene and xylene in ambient air,

Christchurch, 2004/2005. In: Report R05/21

of Environment Canterbury of New Zealand.

http://ecan.govt.nz/publications/Reports/Myles.pdf.

NIOSH, 2003. Hydrocarbons, aromatic: method 1501. NIOSH

Manual of Analytical Methods (NMAM) (4th ed.).

www.cdc.gov/niosh/docs/2003-154/pdfs/1501.pdf-United

States

Pasquale I, Polverino R, Salvestrini S, Capasso S, 2009. Tem-

poral and spatial distribution of BTEX pollutants in the

atmosphere of metropolitan areas and neighbouring towns.

Environmental Monitoring and Assessment, 150(1-4): 437–

444.

Perry R, Gee I L, 1995. Vehicle emissions in relation to fuel

composition. Science of the Total Environment, 169(1-3):

149–156.

Pilidis G A, Karakitsios S P, Kassomenos P A, 2005. BTX mea-

surements in a medium-sized European city. AtmosphericEnvironment, 39(33): 6051–6065.

Truc V T Q, Oanh N T K, 2007. Roadside BTEX and other

gaseous air pollutants in relation to emission sources.


UK DEFRA, 2012. Benzene and 1,3-butadiene concentrations at

the roadside. In: Report of Department for Environment,

Food and Rural Affairs of United Kingdom. http://uk-

air.defra.gov.uk/reports/empire/vocrep/bchpt4.html.

US EPA, 1999. Compendium Method TO-15. Determination

Of Volatile Organic Compounds (VOCs) In Air Col-

lected In Specially-Prepared Canisters And Analyzed By

Gas Chromatography/Mass Spectrometry (GC/MS). http://

www.epa.gov/ttnamti1/files/ambient/airtox/to-15r.pdf.

US EPA, 2012. Benzene. http://www.epa.gov/ttn/atw/

hlthef/benzene.html.

WHO 2000. Benzene. In: Air Quality Guidelines for Eu-

rope (2nd ed.). Copenhagen, World Health Organiza-

tion Regional Office for Europe. http://www.euro.who.int/

−data/assets/pdf−file/0005/74732/E71922.pdf.

Wang P, Zhao W, 2008. Assessment of ambient volatile organic

compounds (VOCs) near major roads in urban Nanjing,

China. Atmospheric Research, 89: 289–297.

Wang P, Zhao W, 2008. Assessment of ambient volatile organic

compounds (VOCs) near major roads in urban Nanjing,

China. Atmospheric Research, 89(3): 289–297.

Wang Y, Ren X, Ji D, Zhang J, Sun J, Wu F, 2012. Charac-

terization of volatile organic compounds in the urban area

of Beijing from 2000 to 2007. Journal of EnvironmentalSciences, 24(1): 95–101.

Xu X, Pereira M, Miller L J, Grgicak-Mannion A, Wheeler

A, 2010. Methods used to detect additional sources using

Toluene/Benzene in Windsor, Ontario (2004–2006). In:

Proceedings of 2010 American Geophysical Union Fall

Meeting: Atmospheric Sciences. San Francisco, California,

USA. 13–17 March.

Documents

BTEX pollution caused by motorcycles in the megacity of HoChiMinh